Systemic Anaplastic Large Cell Lymphoma (ALCL) is the most common T-cell lymphoma in children. ALCL is characterized by its anaplastic cell morphology and high level expression of CD30 on the cell surface. This diffuse and homogeneous CD30 expression in ALCL cells and tumors has been considered as a diagnostic feature for the disease and anti-CD30 antibodies are widely used as a specific diagnostic probe in clinical settings. Developing an antibody is time-consuming and costly and batch-to-batch variations due to usage of different animal or cultured cells are common. To overcome these limitations a chemically synthesized specific probe for CD30 has been investigated. A recent study reported that a synthesized RNA aptamer could specifically bind to CD30 molecules in solution with high affinity. By using cultured lymphoma cells, our preliminary work indicates that this RNA aptamer also binds specifically to human cells via their surface CD30, suggesting that the aptamer may be used as a specific probe to detect ALCL cells for disease diagnosis. Since RNA is an easily degradable molecule when used in routine clinical lab testing conditions;developing a stable RNA aptamer probe is critical for clinical application. Additionally, the usefulness of an RNA aptamer as a diagnostic tool for ALCL would be further enhanced by improving the aptamer's sensitivity/affinity and specificity toward its target. As an initial proof of concept, which can be extended to a commercialized diagnostic product for clinical use;we propose to develop a new RNA reagent building block which can be used to improve the RNA aptamer. Our central hypothesis is that the phosphates of the RNA aptamer backbone play a critical role in its interaction with its target biomarker molecule CD30. Replacing the two non-bridging oxygens with sulfurs at several linkage positions will result in a phosphorodithioated (PS2) RNA aptamer (PS2- aptamer) that will increase the RNA aptamer's stability, cell-binding affinity and specificity. We plan to test our central hypothesis and accomplish the objective of this application by pursuing the following three specific aims: Aim 1. Develop a new chemistry for producing TOM-thiophosphoramidites and a new protocol for synthesis of PS2-RNAs;Aim 2. Develop parallel synthesis processes for PS2-aptamers on a high density chip for high throughput optimization of the anti-CD30 RNA aptamer;Aim 3. Validate specific cell-binding of the optimized CD30 PS2-aptamer and the original RNA aptamer to cultured lymphoma cell lines in vitro. Our ultimate goal is to advance into clinical studies an optimized PS2- aptamer that has excellent affinity and specificity for the CD30 ALCL tumor biomarker. PUBLIC HEALTH RELEVANCE: Systemic Anaplastic Large Cell Lymphoma (ALCL) is a devastating cancer that affects children and is characterized by high levels of the CD30 protein on the cancer cell surface. AM Biotechnologies in collaboration with The Methodist Hospital Research Institute will develop a diagnostic tool for ALCL using a molecule that will bind specifically and tightly to the CD30 protein on the surface of the tumor cells. This molecule will be constructed from a short strand of nucleic acids called an aptamer. Aptamers serve as excellent detection tools because they are extremely sensitive and very specific to the target.